[sharbeldam]

There is a reaction that converts fluorene to fluorenone with a base + stark catalyst and O2, and it converts CH2 to ketone.

When can we use this oxidation? does it have to be allylic/benzylic for it to work since the hydrogen needs to be a bit acidic? also, does it oxidize alcohols too or only allylic/benzylic carbons with hydrogens?


Thanks a lot

[rolnor]

Yes, the protons need to be activated, non-activated alkanes does not react. You can oxidize non-activated arenes with free-radical conditions with Fentons reagent, alkanes give other products.

[sharbeldam]

Thank you rolnor, please allow me to go a little more in depth
1) If i put a strong oxidizing agent like KMnO4 instead of " O2 " in the reaction described above, it will give me ketone as well?
2) If I use the same reagents (O2+strong base+Catalyst) to 2-hexene (which has two allylic carbons) will it give ketone and carboxylic acid on the side then?

[rolnor]

Thank you rolnor, please allow me to go a little more in depth
1) If i put a strong oxidizing agent like KMnO4 instead of " O2 " in the reaction described above, it will give me ketone as well?
2) If I use the same reagents (O2+strong base+Catalyst) to 2-hexene (which has two allylic carbons) will it give ketone and carboxylic acid on the side then?

1. I dont know, its possible
2. No, that is not likely, the protons are not acidic in 2-hexen. I think you need to do some literature search like scifinder. I think you can use selendioxide to oxidize allylic positions.

https://en.m.wikipedia.org/wiki/Selenium_dioxide

[sharbeldam]

Actually just thinking about (1) again, reacting fluorene with KmnO4 (strong oxidizing agent) it should transform every benzylic carbon to COOH. (Aromatic Side Chain Oxidation to Carboxylic Acid). So i guess it's not possible here since I need a fluorenone?

* What is weird, that is in wikipedia it says " Sodium dichromate can be used in fluorene to fluorenone conversion. "
How come? since it is a strong oxidizing agent like KmNO4...

I really am trying to find another oxidizing agent that would do the same thing (Benzlic CH2 to ketone) Like O2/Base

[rolnor]

There could be some other reagent that could do this. People so far has found that you can do it with chrome(VI)oxide, I have oxidized benzylic CH3 to aldehyde this way.
Do you have access to Scifinder or similar?

[sharbeldam]

Thank you, so it's possible to do it with a strong oxidizing agent you are saying? it wont continue to COOH?
No I don't have access, I can check it out, I'd love to get access to sites that will help me know more O-chem.

I found this link that includes all oxidations of benzylic to ketones but it's still complicated,only 1 reaction contains a compound with two aryls like fluorene and the reagent is still O2 with base :/ haha.

https://www.organic-chemistry.org/synthesis/C2O/ketones/oxidationsbenzyls.shtm

[rolnor]

Thank you, so it's possible to do it with a strong oxidizing agent you are saying? it wont continue to COOH?
No I don't have access, I can check it out, I'd love to get access to sites that will help me know more O-chem.

I found this link that includes all oxidations of benzylic to ketones but it's still complicated,only 1 reaction contains a compound with two aryls like fluorene and the reagent is still O2 with base :/ haha.

In my case I used acetic anhydride as solvent and then you get the acylal, a acetal with two acetoxygroups. So the aldehyde is protected from oxidation to COOH, you  then get the  aldehyde by hydrolysis of the acylal so its twoo step procedure.

https://www.organic-chemistry.org/synthesis/C2O/ketones/oxidationsbenzyls.shtm

[sharbeldam]

Thanks rolnor for your help.
Just wanna add something I found today since many people come to this site and in the future there could be students whom search for benzylic carbon oxidation to a ketone.

https://shodhganga.inflibnet.ac.in/bitstream/10603/9889/11/11_chapter%203.pdf

This book explains a facile way of doing that by converting a benzylic carbon (CH2-R) to ketone by reacting it with DIB/NaN3, they tested many solvents, and the solvent that gave the most yield was CH3CN/H2O.

[rolnor]

Thanks rolnor for your help.
Just wanna add something I found today since many people come to this site and in the future there could be students whom search for benzylic carbon oxidation to a ketone.

https://shodhganga.inflibnet.ac.in/bitstream/10603/9889/11/11_chapter%203.pdf

This book explains a facile way of doing that by converting a benzylic carbon (CH2-R) to ketone by reacting it with DIB/NaN3, they tested many solvents, and the solvent that gave the most yield was CH3CN/H2O.

Very good reading, thank you!

[hollytara]

It is apparent that benzyl C-H and C-C bonds are different than normal alkyl C-H and C-C bonds; they are not as strong, more easily broken since the resulting benzyl radical or cation is stabilized.  Fluorene is even more so since it is conjugated to two benzene rings! 

There are a lot of different reagents that convert fluorene to fluorenone - the oxidation can be performed with air using the right catalyst.  It is sometimes done as an undergraduate lab.  Some reagents are too strong and will open the fluorene ring and generate a biphenyl carboxylic acid - KMnO4 can do this, especially at higher temperatures. 

A quick web search will reveal a lot of reports of different reaction conditions that will give fluorenone from fluorene.

[rolnor]

It is apparent that benzyl C-H and C-C bonds are different than normal alkyl C-H and C-C bonds; they are not as strong, more easily broken since the resulting benzyl radical or cation is stabilized.  Fluorene is even more so since it is conjugated to two benzene rings! 

There are a lot of different reagents that convert fluorene to fluorenone - the oxidation can be performed with air using the right catalyst.  It is sometimes done as an undergraduate lab.  Some reagents are too strong and will open the fluorene ring and generate a biphenyl carboxylic acid - KMnO4 can do this, especially at higher temperatures.


A quick web search will reveal a lot of reports of different reaction conditions that will give fluorenone from fluorene.

Did you read the posts above hollytara? The example with air and catalyst is mentioned.